1. Field of the Invention
The present invention relates to an image processing apparatus used in an image forming apparatus such as an MFP, and to an identification method for a line pair pattern that includes a line screen pattern.
2. Description of the Related Art
An image forming apparatus that forms images using the electrophotographic method, such as, for example, a photocopier, a printer, a facsimile, and an apparatus with multiple functions (called an MFP, or multi-function peripheral), may be provided with an image processing apparatus that performs a halftone region identification process to identify halftone regions in a document, enabling the image processing apparatus to execute a smoothing process for preventing the occurrence of moiré patterns during printout (see Patent Document 1: JP 2006-287603A).
Focusing on the characteristic that halftones are made up of individual dots, the stated halftone region identification process identifies the individual dots in an inputted color image, and determines whether or not those individual dots constitute a halftone.
There is proposed a method for detecting an inclination of an image obtained by reading an original (see Patent Document 2: JP2003-076993A). The method involves calculating an angle at which straight lines are concentrated based on coordinate conversion values of pixels of a binary image or a multi-valued image, and detecting the inclination of the image based on the calculated angle.
However, the method disclosed in Patent Document 1 cannot detect the individual dots found in line screen patterns (line screen shapes) in which individual dots have been linearly connected, line pair patterns (line pair shapes) configured of plural line screen patterns that have been arranged evenly, and so on, and therefore cannot identify such line screen patterns and line pair patterns as halftones (halftone regions).
As a result, the smoothing process is not executed on the line screen patterns and line pair patterns that could not be identified as halftones. In addition, there are cases where line screen patterns and line pair patterns that have not been identified as halftones by the region identification process are identified as characters, and the edges thereof are enhanced in a subsequent edge enhancement process.
For this reason, a noticeable visual difference arises between regions identified as halftones and on which smoothing has been carried out, and regions which are halftones but have had edge enhancement carried out rather than smoothing (that is, the stated line screen patterns and the like).
The method disclosed in Patent Document 2 causes the increase in data amount and processing time, because the method involves performing coordinate conversion on each pixel of an inputted image.